Spinner A has numbers 1 to 4 on it. Spinner B has numbers 1 to 3 on it. Both spinners are spun and the numbers on each are added together to give a score.

Question

What is the probability that the score will be
a) 7?
b) 3 or 4?

Answer 1

Spinning each spinner is an independent event and we know that there are 4 x 3 = 12 different permutations of 2 numbers we can get from spinning the 2 spinners. 

 

Of the 12 permutations only 1 (4,3) will get us a sum of 7. Therefore the P(score=7) = 1/12

 

Of the 12 permutations the following will sum to 3 or 4: (1,2) (1,3) (2,2) (3,1) (2,1). So P(score = 3 or 4) = 5/12